1. Field of the Invention
The present invention relates to a sonar transducer. More particularly, but not by way of limitation, the present invention relates to a digital sonar transducer which includes circuitry for firing a sonar pulse and receiving sonar echos.
2. Background of the Invention
Sonar devices are well known in the art and find widespread use in sport fishing, navigation, scuba diving, as well as any number of other recreational or commercial activities. Typically, a sonar system will include a sonar unit, which includes a display for providing information to the operator, and a transducer which is mounted under the waterline for generating an ultrasonic pulse and receiving echoes from objects in the water, or the bottom surface. The electronic circuitry for driving the transducer to transmit an acoustic pulse and for amplifying and filtering received echoes has traditionally been located in the sonar unit. Locating such circuitry in the sonar unit has, heretofore, provided a number of advantages, such as: there is more likely to be ample room for the circuitry in the sonar unit while the transducer tends to be comparatively small; the environment of the sonar unit is relatively benign, at least when compared to the environment of the transducer; and the cost of replacing a lost or damaged transducer is less when its associated circuitry is located remotely.
In such a system, driver circuitry in the sonar unit produces a pulse consisting of a packet of several cycles of an ultrasonic signal at a fairly high output power. This pulse is delivered to the transducer via a coaxial transmission line. After transmission of the sonar pulse, the transducer is typically used to xe2x80x9clistenxe2x80x9d for echoes. Received echoes produce very small signals, on the order of a few millivolts, which are sent via the coaxial transmission line to receiver circuitry in the sonar unit. In the sonar unit, the received echoes are amplified, filtered, and analyzed.
Thus, a great deal of momentum has been built around placement of the sonar transceiver circuitry into the sonar unit and, indeed, existing sonar systems, have served the sport fishing industry well. However, the evolution of other boating systems, as well as the advancement of sonar technology, have altered the equation to the point where the advantages associated with placing transceiver circuitry within the transducer, and the problems associated with the traditional method, far outweigh the advantages mentioned above.
First, electromagnetic interference from other systems poses a significant problem for sonar systems. As previously mentioned, echoes received by the transducer generate very low level signals which must be transmitted through a coaxial cable to the sonar unit. This signal is susceptible to interference from electromagnetic noise, ground noise, radio frequency noise, and the like. Such noise often induces voltages in the cable which interferes with legitimate echo signals. While the received signal may be filtered at the sonar unit to remove much of the unwanted noise, some noise will likely be indistinguishable from legitimate echoes and cannot be removed by filtering. In particular, pulse width modulated trolling motors are notorious for producing large amounts of electromagnetic noise. However, communication systems, engine ignition systems, and other computerized gear may also create significant levels of interference. Eliminating the need to send low level signals from the transducer to the sonar unit could virtually eliminate interference caused by the various sources of noise. Furthermore, transmitting a digital representation of the echo signals could eliminate the effects of noise induced in the cable.
In addition, it is widely accepted that some sonar frequencies are better suited for a particular purpose than other sonar frequencies. While most low and moderately priced sonar units operate at only a single frequency, and some high-end units add a second frequency, recreational sonar units operate at frequencies which represent a compromise designed to serve the sport fisherman reasonably well. Not only does a broader selection of frequencies allow tailoring of a sonar system for a particular environment, it allows multiple units to be used in a small area. Presently, when multiple units operate at a single frequency within a small area, the sonar systems tend to interfere with one another. In contrast, multiple units operating at spaced-apart frequencies can be operated in a small area without significant interference between units.
Finally, wiring between the sonar unit and the transducer has been problematic, often requiring a skill level far beyond that of the typical purchaser of a sonar system. The cabling must be routed to: avoid leaks since the sonar unit is invariably above the water line, inside the boat, while the transducer is invariably below the water line, outside the boat; avoid trip hazzards, especially in environments where tripping could result in a man overboard, and in consideration of the fact that the cables are typically only available in discrete lengths; and to avoid damage to the cable. In addition, fishing boats often have multiple electrical systems for the use of an electric trolling motor which can further complicate wiring considerations.
Recently, sonar transducers having integral transmitter and receiver circuitry have been available. Unfortunately, such transducers have thus far been output-only devices and are not be controllable by a sonar unit. The transducer simply fires at-will and at a predetermined power. The sonar unit cannot adjust the power, repetition rate, duration of the sonar pulse to adjust to the environment or synchronize the sonar output to other devices. In light of environmental factors such as varying reflectivity of different bottom surfaces, and the differences in the demands of the particular uses for a sonar system, i.e. navigation, fish location, searching for objects, etc., the inability to control the transducer output is unacceptable.
Thus it is an object of the present invention to provide a sonar transducer which includes transceiver circuitry within the transducer to alleviate the problems and overcome the limitations discussed above.
The present invention provides a digital sonar transducer having transmitter, receiver, and computing circuitry associated with the particular transducer located remote to a sonar display unit. In a preferred embodiment, the digital sonar transducer receives commands via a digital input and sends echo information via a digital output. The inventive transducer includes: an acoustic transducer element configured to emit a sonar pulse and to receive sonar echoes; transmitter circuitry for driving the transducer element to generate a sonar pulse; receiver circuitry to amplify and condition received echoes; a computing device to process the echo information and interface circuitry to digitally communicate with a sonar display unit.
In one preferred embodiment, the transducer and its associated receiver and transmitter circuitry are housed within a common, waterproof housing. Like its prior art counterparts, the transducer is secured to the boat below the waterline and wiring is routed to the transducer in an appropriate manner in light of the environment. Unlike prior art transducers, shielded cable is not required to carry the sonar signal.
In another preferred embodiment, the transducer receives commands digitally via the interface, adjusts the power of the transmitter in response to the commands, transmits an acoustic pulse, adjusts the receiver gain, filters and discriminates incoming echoes, and transmits echo information digitally via the interface. Since the input and output signals are digital in nature, they are relatively immune from the effects of electromagnetic, and electrical, noise.
In still another preferred embodiment, the inventive transducer may be made available in an array of different frequencies such that: 1) a recreational sonar may be xe2x80x9ctunedxe2x80x9d to a particular frequency which is especially well suited for use in a particular environment; and 2) multiple sonar systems may be simultaneously used on a single boat or in a small area in an asynchronous manner without interfering among themselves. Since the resonant element and the driver circuitry are both parts of transducer, there is no need to frequency match a transducer to a particular control unit.
In yet another preferred embodiment, the inventive transducer is provided with a wireless interface to reduce the complexity of wiring the sonar system. Preferably, in such a system, the sonar transducer is battery operated such that no wires need to run through, or over, the hull.